The invention relates to a method for producing a gas-tight plastic closure for containers by two-component injection molding. Such a method is known from U.S. Pat. No. 4,754,892. Two-component injection molding of such a type is performed in a molding station comprising a concave mold form in a first tool portion and a mold core in a second tool portion. The tool portions create a first cavity and are displaceable with respect to one another at a predetermined separation plane. The known cap is produced by injecting flowable thermal plastic material through a runner into the first cavity. The known runner is located in the mold form tool portion, not in the separation plane between the mold form and the mold core.
The inner core of the known molding device is rotated so as to move downward. The U.S. patent teaches that an excentric pin moves out of the end panel wall leaving a passage. This rotational movement is objected by the cap body and may result in a damage of the cap.
In addition, the known core is fully moved out of the mold form. Thereafter, the cap is ejected from the mold form. This type of deforming and ejecting requires completed rotation of the mold core which is an uneconomically complex and time-consuming movement in mass article production.
U.S. Pat. No. 4,803,031 discloses another two-component injection method for closure caps. In a first injection phase, a lower molding head is illustrated in its raised position with a tight engagement between a plunger and an upper die member in a position defining a sealing member. A softer plastic for the sealing member is injected from a nozzle outlet into the sealing member cavity. Thus, the sealing member is molded as a first component. This nozzle outlet and another nozzle outlet are not in a central position and are not released during the dropping of the plunger. The entire lower die head is lowered and the second nozzle outlet is used to fill the resulting cavity comprising the cover and the skirt portion of the closure cap. Lowering of the lower die head occurs, before the retaining means of the cap body have been molded. Finally, the molding plunger is unscrewed from the closure. There is no support of a final ejection of the plastic closure from the mold core by an axial displacement of a central tool element of the mold core.
In Applicant's co-pending U.S. patent application Ser. No. 07/443,082, protection is sought for a method for producing an airtight plastic closure for bottles and similar containers, in which two-component injection molding is employed.
The method is used in a manner such that the mold form is configured in the form of the actual closure cap, where the interior space of this closure cap is complementarily enclosed by the mold core in the usual manner. According to the method suggested in that application, the mold core is then displaced by a predetermined amount relative to the first molding and the second substance is injected through a central injection feeder into the so created intermediate space. This second substance is usually designed as a sealing member with respect to the bottle to be closed.
The method described in that patent application, which uses two-component injection molding, has great advantages for producing plastic closures for bottles and similar containers, which arise both in the production and also in the later use of such closures.
According to the above-described method, it remains up to the skilled person how he performs the relative movements of the mold core. Since bottle closures usually are provided with retaining means like threadings on the inside, with which they can be screwed onto the bottle to be closed, it would be possible to screw back the mold core by a predetermined amount from the previously molded closure, and then to inject the second substance into the so created intermediate space.